The present invention relates to a modular machine tool for machining series of parts from a bar of raw material, said machine comprising at least one module equipped with at least one machining station, a device for tranporting and maintaining the bar of material in position, and a device for indexing said bar, said machining station comprising at least one machining unit equipped with independent drive means designed for displacing said unit with respect to the bar of raw material.
Modern machine tools of the numerically controlled type, wherein the parts to be machined undergo computer-controlled linear or circular transfer, may be considered as improvement derived from conventional machine tools wherein the parts to be machined are positioned and then withdrawn manually. However, the general principles underlying these two generations of machines remain the same. Thus, in both cases, the raw material is cut up, possibly preworked to form a blank which is next placed in pre-positioning elements designed to maintain it in position when machining, and is then machined to obtain the final part. The prepositioning elements consist of jigs adapted to each particular part to be machined. These jigs must be designed and made according to the parts and can generally not be reutilized for other parts.
The numerically controlled machines moreover necessitate linear or circular transfer units comprising complicated mechanisms which must be adapted to the form and dimensions of the parts to be machined.
These well known problems result in a limitation of the production rates and lead to a relatively high cost of machining the parts in spite of the automation of transfer and machining of the parts.
The complexity of these machines essentially designed for manufacturing large series of parts moreover renders setting up the manufacture of each new series of parts slow and complicated and considerably reduces the flexibility of their use, so that the plant is forced to manufacture great amounts of parts and to thus constitute important stocks, which often involves a non negligible risk for the plant management.
In order to simplify the transfer operations and facilitate transition from one series to another, modular machines have been designed, comprising several machining modules which may be changed and prepared in advance for a new manufacturing operation.
For example, Swiss patent CH-A No. 500 809 describes a modular machine tool of the type indicated in the preamble, comprising a frame provided with rails along which several slides are distributed and respectively carry on one hand a machining module and on the other hand means for supporting and transporting the bar of raw material. The machining modules may operate independently of each other. They are freely mounted by means of springs on their respective slides and they are positioned with respect to the bar by means of conical indexing rods which are engaged in indexing holes provided in the bar.
However, this machine has certain drawbacks. Mounting the machining modules on the slides circulating on a common track does not permit the number and/or the disposition of the modules to be readily modified or to readily replace one of them. Moreover, the utilization of special slides for supporting and advancing the bar complicates the machine, increases its length and raises the loss of material at the extremeties of the bars. On the other hand, the support device does not permit fixing the machining unit with respect to the bar in a sufficiently rigid manner to permit the use of a machining unit which is mobile along three orthogonal axes. Another drawback is the fact that the rails receive the chips and are dirtied.